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Petrochemical data for the igneous rocks in and around the Erdenetiin Ovoo Porphyry Cu-Mo deposit, Orkhon Selenge trough (part of the Mongol Okhotsk Fold Belt) are re-examined. Magmatic activity of the trough started by Permian bimodal volcanism formed in extensional regime changed in early Mesozoic by compressional regime by intrusion of calc-alkaline gabbro-granodiorite-granite of the Selenge Intrusive Complex with subsequent intrusion of Porphyry Association followed by trachybasalt-trachyandesite alkaline series volcanics of the Mogod Formation. Permian volcanics exhibits typical continental arc characteristics, the Selenge Complex intrusion and Porphyry Association are related to calc-alkaline, I-type, magnetite series, medium and high K rock, and enriched in LIL, depleted in Nb, Ta, Ti and P that typical for continental arc environment. The Mogod Formation is characterized by variation in K, enrichment in Al and LIL, depletion in Nb, Ta and Ti, showing magmas derived from a sub-arc mantle source. Petrochemistry and low initial 87Sr/86Sr isotope ratio of intrusive rocks are corresponding to the adakitic nature and consisting with arc condition. © 2007 American Institute of Physics [ABSTRACT FROM AUTHOR]